First, I need to define what I mean by an "assault rifle", as there are various definitions around. The one I use is:

"A standard military rifle,
capable of controlled, fully-automatic fire from the shoulder, with an
effective range of at least 300 metres".

This has some clear implications
for the ammunition such weapons are chambered for. First, it excludes
all weapons designed around pistol cartridges (i.e. machine pistols and
sub-machine guns - SMGs) as they only generate around 500 joules muzzle
energy and cannot meet the range requirement. Second, it excludes the
traditional "full power" military rifle/MG cartridges such as the
.303", the .30-06, the 7.92x57, the 7.62x54R and the 7.62x51 NATO
(typically firing 10-12g bullets at 750-850 m/s and developing around
3,000-4,000 joules), as these are so powerful that their recoil is
virtually uncontrollable in fully-automatic rifle fire from the shoulder.

Pistols such as the Mauser C96
(7.63x25) and P08 Luger (9x19 Parabellum) produced carbine derivatives
with detachable stocks, usually only capable of semi-automatic fire but
a few with a burst-fire option. These were relatively expensive to
make, however, so the future in short-range automatics lay with the
much simpler API blowback SMG. The first of these in service (if you
discount the curious twin-barrel Villar Perosa) was the Bergman MP18 in
9x19, which was the ancestor of the MP 38/40, the Sten Gun, the PPSh
and so on. An honourable mention also to the Thompson, developed
separately in the USA from 1916 onwards for their .45 Auto cartridge.
An oddity was the Pedersen Device of 1918, which replaced the bolt in
the US Springfield Rifle with a semi-automatic mechanism to fire small
.30 cal (7.62x20) pistol-type rounds developing less than 400 joules;
it was never used in anger.

Attempts to improve the power and range of the
SMGs, such as the
development of the .45 Remington-Thomson in the experimental Model 1923 Thompson SMG
(which used a very powerful loading developing almost three times the muzzle
energy of the .45 Auto) and the use of the 9x25 Mauser round in the
1930s Solothurn S1-100 and
Hungarian Kiraly 39M and 43M SMGs (which saw some service), did not catch on. There is a limit to
the degree to which the performance of such weapons can be increased as their
large-calibre, relatively light and round-nosed bullets lose velocity quickly.
Also, the basic API blowback system used by most SMGs is not suited to high-powered
ammunition, although the Kiraly and Thompson M1923 had more sophisticated mechanisms.

More recently, small-calibre high-velocity
PDW ammunition has emerged (described in more detail in THIS
article). The FN 5.7x28 has achieved some sales, in both the Five-seveN pistol and the P90 SMG,
as has the rival HK 4.6x30 in the MP7. However, despite their improved range
performance, these cartridges only develop around 500 joules so don't qualify as assault
rifle ammunition. The Chinese 5.8x21 DAP-92 is even less powerful.

Although
a self-loading rifle did not enter general service as a standard
infantry rifle until the US M1 Garand became available in 1937, there
were many earlier models, some of which are shown below. However,
attempts to make such weapons fully automatic ran into difficulties due
to the power of their cartridges. Perhaps the most famous example
was the German FG 42 paratroop rifle in 7.9x57. Some of the early
rifles in 7.62x51 NATO, such as the American M14, German G3 and some
versions of the FN FAL, were also capable of fully automatic fire, but
the recoil problem made them incapable of accurate fire on full-auto so
they cannot be classified as assault rifles. The most successful
attempt at this was probably the Swiss Stg.57 in 7.5x55 but this was
significantly heavier than contemporary rifles, the weight helping to
absorb the recoil. The American Browning Automatic Rifle (BAR) in
.30'06 was very controllable but this was even heavier, weighing about
twice as much as a "standard military rifle", so is excluded by the
definition.

Assault
rifles therefore need to be designed around a cartridge intermediate in
power between pistol and full-power rifle rounds; in practice,
approximately in the 1,250-2,500J range depending on the calibre. There
have been two contrasting approaches to the design of a suitable
intermediate cartridge with the appropriate compromise between long
range and light recoil. One is to retain the same 7.5-8mm calibre as
the full-power round, but with a shorter cartridge case firing a
lighter bullet at a lower muzzle velocity (lets call these "full
calibre assault rifle", or FCAR, rounds). The other is to reduce the
calibre while retaining the same, or a higher, velocity (reduced
calibre, or RCAR rounds). FCAR
rounds score well in the traditional methods of measuring barrier
penetration and terminal effectiveness (dominated by calibre and bullet
weight) and also by being less affected by the bullets striking foliage
etc on their way to the target. However, they have a relatively steep
trajectory and a rapid velocity loss due to the short, fat bullets,
which quickly reduces their effectiveness at long range.

Above: the full-power
7.9x57, 7.5x55, .30-06 and 7.62x51, shown next to the 7.62x39 and 5.56x45
which illustrate the most common FCAR and RCAR rounds respectively

A decision to reduce the calibre raises
the immediate question; by how much?

At
the large end of the RCAR scale (7mm), bullet weight and muzzle
velocity can be much the same as in the FCAR cartridges, but the better
ballistic coefficient due to the longer and more slender bullet will
reduce velocity loss and improve long-range performance. As the calibre
decreases, so the recoil and the ammunition weight become lighter and
the velocity can be higher, thereby flattening the trajectory; all good
things. The downside is that barrier penetration may be reduced and
stopping power becomes more controversial (relying on velocity and
rapid bullet yaw on impact rather than calibre and bullet mass; which
according to combat reports sometimes works, sometimes doesn't). The
long-range performance also begins to decrease as small-calibre bullets
generally have poorer sectional density ratios, and thereby ballistic
coefficients, than large-calibre ones.

Different
nations have made different choices in developing assault rifles, and
the purpose of this article is to describe and analyse them in order to
examine the future prospects for this type of weapon.

Developments up to 1918

The
elements of an assault rifle were in place surprisingly early in the
history of automatic weapons. Self-loading rifles were developed before
the end of the 19th Century and the first selective fire (semi or full
auto) rifle using a medium-power cartridge was probably the Italian
6.5mm Cei-Rigotti, developed between 1900 and 1905, but this was not
adopted. Mannlicher introduced a Self-Loading Carbine in 7.65x32
calibre, an improved and enlarged version of their Model 1901 pistol
carbine chambered for a lengthened version of the 7.63x25 pistol round,
which was made in about 1904. It never went past the prototype stage
and its ballistics are not known. However, the cartridge case is
similar in length as well as calibre to the US .30 M1 Carbine's, but
slightly fatter as it is bottle-necked.

The
first service weapon which can be identified as conforming to the
specification of an assault rifle dates back to the First World War;
the Russian Federov Avtomat of 1916. This was a selective fire
weapon using a short-recoil action. It was originally chambered for
Federov's own purpose-designed high-velocity 6.5mm cartridge, but
as the Great War was then underway there was no chance of a new
cartridge being adopted, so he modified his gun to use the Japanese
6.5x50SR Arisaka cartridge, large quantities of the guns and ammunition
having been acquired by Russia to meet a shortfall in their supply of
rifles. This was an excellent choice, as the cartridge combined
moderate recoil with a good long-range performance, but only a few
thousand Avtomats were made. They were used in action in the Russian
Civil War and also as late as the Winter War with Finland in 1939-40,
and thereby earned their place in small-arms history.

Above: Federov Avtomat

8mm Ribeyrolles

It can be argued that neither the Cei-Rigotti nor the
Federov Avtomat used "intermediate" cartridges, as the 6.5mm Carcano and Arisaka
were the front-line rifle/MG rounds in the Italian and Japanese armies
respectively. This is true, but it is worth bearing in mind that, in terms of
calibre and muzzle energy, they were in the same class as the present-day 6.8x43
Remington SPC and 6.5x38 Grendel, which are today regarded by many as ideal
intermediate cartridges for assault rifles.

The French also nearly made it into the record books with
the first selective-fire rifle using purpose-designed intermediate ammunition.
During WW1 they made some use of the semi-automatic Winchester Model 1907 in
.351 and the Model 1910 in .401 Win SL (self-loading) cartridges; the rifle design was very
simple, being blowback only. While these were mainly used by aircrew, in 1917
France placed an order for 2,200 of an automatic version of the M1907 for use by
special assault soldiers. At the same time, they were modifying the .351 SL
cartridge by necking it down to accept an 8mm rifle bullet, creating the 8mm Ribeyrolles
– arguably the first purpose-designed intermediate military cartridge. This was
tested in July 1918 and found to be effective out to 400m. The war
ended before anything came of this, but it is not hard to see that had it lasted
for another year or two, French troops could have been equipped with an assault
rifle. As it was, neither the Ribeyrolles, nor a 7mm version designed in the
1920s, made further progress.

Another
very interesting
weapon and ammunition combination which emerged in 1918-19 was the
Winchester Machine Rifle in .345 calibre, designed by Frank Burton. The
cartridge was simply the .351 Win SL loaded with a pointed 11.2g (173
grain) bullet fired at a muzzle velocity of 564 m/s (1,849 fps). The gun weighed 4.5 kg (10 lb) and
was 116 cm long (45.5") with a barrel length of 63.5 cm (25"). It used a blowback action and fired from an open bolt; it had selective fire, with a cyclic rate on automatic of 800 rpm. The most interesting
aspect was the unique ammunition feed, which consisted of two box
magazines, top-mounted but in a vee-form or butterfly wing layout. The
capacity of each magazine is commonly said to be 40 rounds, although
the Winchester museum (which has the only surviving example) states 25
rounds. This layout had several advantages over other top-mounted magazine feeds:

Interest in assault rifles on the part of the major powers
then largely disappeared from view until the Second World War, although
experiments continued in some smaller countries, especially Switzerland. Their
prolific gun designer Fürrer produced a short-recoil carbine with a new
bottle-necked 7.65x35 cartridge in 1921. We are now getting very close to the
concept – except that the cartridge had a round-nosed rather than pointed
bullet. A year later a modified 7.65x38 appeared which did have a pointed
bullet. Swiss sources indicate that data from the tests of these rounds were
passed to DWM in Germany, where they may have influenced later developments.
Other pre-Second World War Swiss short-case ammunition designs included a
different and rather mysterious 7.65x38 round for which unloaded components were
made in some quantity, for an unknown destination, just before the war.

In
Italy the Terni Model 1921 selective-fire carbine emerged: the
cartridge was a 7.35x32 rimless round, a shortened and necked-out
version of the standard 6.5x52, which fired a pointed 8.7g (134.5
grain) bullet at a claimed 600 m/s (1,970 fps). In the
early 1930s, the US Frankford Arsenal tested this
rifle, or one very like it. Various
other Italian experiments took place throughout the interwar years, but
to no effect: the 7.35x51 round eventually selected was designed to be
used in rebarrelled 6.5mm weapons (they increased the calibre because it was cheaper to rebore existing worn-out barrels instead
of buying new ones), but it was at least loaded to quite modest levels in recognition of the fact that long range was not required.

In 1925 Kynoch of the UK proposed a "7mm light automatic rifle cartridge"
intended for BSA. The factory drawing shows a bottle-necked case with a length
of 41mm and a round-nosed bullet. It is not clear whether the cartridge or gun
were ever built.

In Russia, Federov continued to argue for the adoption of a smaller cartridge
than the 7.62x54R. In the late 1920s he recommended adoption of the 6.5 mm
calibre "if not even smaller" and a rimless or semi-rimmed case with a length
shortened by about 20 % (to 40 mm). His ideas were supported in 1930 by V.E.
Markevich, of the Red Army's Weapons Scientific and Research Range, who pointed
out that an ideal cartridge already existed – in the .25 Remington! The .25's
bigger brother based on the same case, the .30 Remington, was used much later as
the starting point for the development of the 6.8mm Rem SPC.

In the early 1930s Denmark made limited numbers of the
delayed-blowback Weibel (or Danrif) M/32 assault rifle in a 7x44 calibre. From
this rifle, the 8 gram (123 grain) bullet reportedly achieved a muzzle velocity
of 750 m/sec (2,460 fps) for a muzzle energy of 1,653 ft-lbs. In 1939 a light automatic
weapon was advertised in Greece in 7.92x36 calibre, the cartridge apparently
being based on a shortened and necked-out 6.5mm Mannlicher case.

In fact, despite the evidence
that most shooting during WW1 was at short range, armies continued to
show an interest in full-power rifle/MG rounds. The Japanese Army began
to replace their 6.5x50SR cartridge with a new 7.7x58 calibre, although
they never completed the changeover. The Italians were similarly caught
at the start of WW2 part-way through a change from their 6.5x52
Mannlicher-Carcano rifle to a 7.35x51 calibre. This happened for
several reasons. One was that long-range MG fire was considered
essential: the first Japanese Army 7.7mm round was only available in
MGs (the first 7.7mm rifles only emerging about a decade later), and
other powerful MG rounds (e.g. the 8mm Breda, 8mm Bofors and 8mm
Solothurn) were introduced during this period.

For the most
part, the introduction of rifles in the new MG calibres seems to have been
to simplify ammunition supply arrangements, rather than because the smaller
calibre rifles were felt to be ineffective.

Finally,
the need for a full-auto rifle (and therefore lower-powered ammunition
with less recoil) was not recognised and probably generally resisted,
on the grounds of economy (automatic rifles being much more expensive
and requiring more maintenance than bolt-action ones), and also the
fear that soldiers would just spray ammunition around at a great rate,
causing increased cost and supply problems (this latter concern was, of
course, fully justified, but has been addressed by improving supply
arrangements). So even the one nation wealthy enough to afford an
automatic rifle - the USA - restricted the M1 Garand to semi-auto fire,
and full-power rounds biased towards MG use prevailed.

There
had been some efforts towards considering intermediate calibres, with
the US Ordnance Board sponsoring comparative trials in the early 1930s
of the effectiveness of different rifle cartridges using anaesthetised
pigs and goats to assess wounding effectiveness. They concentrated on a
.256 (6.5mm), a .276 and the existing .30. The .256 (8g at 820 m/s, for
2,700J - much more powerful than the .25 Remington) most impressed the
testers, but the Board chose the .276 Pedersen (7x51) a medium-power
round developing 2,400J (similar in power to the 6.5mm Arisaka, the
later 7x43 British and the modern 6.8mm Remington), which would have
made an effective assault rifle cartridge. However, the army was still
thinking in terms of long-range semi-automatic fire, a mindset which
did not change until the 1960s. The .276 cartridge was rejected in
1932, partly for cost reasons but also because it did not offer
sufficient long-range performance

World War 2 to 1960 - the Assault Rifle Emerges

In the run-up to World War 2, the focus switches to
Germany. In
the aftermath of the Great War a Hauptmann Piderit of the German Rifle
Testing Commission had advocated a short-cased cartridge and a suitable
rifle to fire it, but his was a lone voice. It wasn't until 1927 that
DWM (actually, the "Berlin-Karlsruher Industriewerke A.G." as DWM was
known between 1922 and 1936) carried out the first tests of short-cased
cartridges, possibly as a result of the data they had received about
the Swiss rounds, but these had no direct result. It wasn't until the
mid-1930s that serious work got underway, and over the next decade no
fewer than five German companies were involved in developing
short-cased cartridges suitable for assault rifles: Geco, DWM, RWS,
Rheinmetall-Borsig and Polte.

Geco was the first in the field, co-operating with the gun company Vollmer-Werke
Maschinenfabrik to produce the Vollmer SL Model 35 self-loading carbine in a
nominal 7.75x40 calibre (the calibre was actually 7.9mm, with a bullet 8.05mm in
diameter). This was officially tested with good results, but led to no orders.
In 1942 Geco produced a new cartridge also intended for a Vollmer carbine, the
7x45SR. This used a wider case and was far more powerful, with a muzzle velocity
of 1,000 m/s. Another cartridge, measuring 7.9x33.5, was designed at Geco and
attributed to an H.G.Winter, a director of the firm, but the date and the gun
for which it was intended are not known.

DWM designed a 7x39 cartridge in the mid-1930s, for which a Walther self-loading
carbine was reportedly made. It was appreciably more powerful than the later
7.9x33 Kurz. However, the interest of the Heereswaffenamt (HWA) was by then
focused on Polte developments, so the DWM round also failed to progress further.
RWS produced several short-cased rifle rounds in the 1930s, including an 8x45,
8x46 and 7x46, but these developments were taken no further. Rheinmetall-Borsig
were involved in a number of prewar experiments concerning 7mm rounds in various
case lengths, some of them very long, probably for high-velocity aircraft gun
projects. One drawing has been found of a 7x36 cartridge which would obviously
have been suitable for assault rifles, but there is no evidence that it was
made. The design work may have been done by Polte on behalf of
Rheinmetall-Borsig.

This brings us to Polte Patronenfabrik of Magdeburg, who made by far the most
significant contribution. The HWA awarded them a contract, probably in 1938, for
the development of a short-cased infantry cartridge. This resulted in several
different designs of cartridge; 7.9x45, 7.9x30, two different 7.9x33 and a 7x45,
all by 1940. In all of these, Polte retained the base diameter of the
standard 7.9x57 rifle/MG round, and in all but the 7mm the same calibre as
well. This kept production costs to a minimum and no doubt helped to account for
the success of their proposals. The final 7.9x33 design (which had less case
taper than the first or "transitional" effort) was approved in December 1940,
the only subsequent change being to the angle of the extractor groove, which was
altered from 45 to 60 degrees in May 1942.

The MKb42(H) by Haenel and the MKb42(W)
by Walther were designed around the new cartridge and produced in some numbers
for field testing. This led to the
development of the Haenel MP43/44 (later renamed
StG 44 for Sturmgewehr or assault
rifle).

The author shooting the MKb42(W) at MoD Defence Academy

Below: the StG 44

Despite initial opposition from
Hitler, this was the weapon the Army wanted to back-up their MG 42
GPMGs and it was produced and used in quantity, with nearly half a
million made. However, the end of the war stopped the direct line of
development of this significant weapon.

At the same time as the German work was reaching its
conclusion, the USA was developing the .30 M1 Carbine, a light rifle chambered
for a new 7.62x33 straight-cased round based on the old .32 Winchester SL
commercial case.
This was not intended as an assault rifle but as what would now be called a
"personal defence weapon" for troops who would not normally carry a rifle.
However, its handiness meant that some front-line troops carried it in
preference to the much bigger and heavier .30 M1 Garand rifle. The M2 version of
the Carbine introduced selective fire and was close to the specification of an
assault rifle, but the cartridge with its round-nosed bullet was really too
small and weak to reach out to 300m (330 yards), considered the desirable
effective range as some 90% of fire-fights took place within that distance.

Attention now switches back to the USSR. The key date was
15th July 1943 when a meeting was held of the Technical Council of the People's
Commissariat for Armament (NKV). They had met to consider "New foreign weapons
firing lower-powered rounds" and studied examples of both the US .30 M1 Carbine
supplied by the USA, and the German MKb 42 (H) in 7.9x33 which had been
captured while undergoing troop trials. The meeting concluded that the new
German gun and cartridge were important developments and decided that a new
reduced-power round must be designed. Responsibility for this was handed over to
the OKB-44 design bureau, which produced the first prototype of what became the
7.62mm M1943 round only a month later, with the first batch of ammunition loaded
with flat-based lead-cored bullets being range-tested that December. This kept
the same calibre as the 7.62x54R rifle/MG round for production convenience, but
adopted a new case which was slimmer than that used by the 7.92x33. A pilot
series-production run began in March 1944, and before the end of the war the
round was combat-tested in prototypes of the Degtyarov RPD light machine gun and
Simonov SKS semi-automatic carbine. At that time the case had a length of 41mm,
but development work continued, resulting in a boat-tailed bullet shape being
adopted and the lead core being replaced with mild steel. The case neck was
reduced to the final 38.7mm to keep the overall round length the same despite
the longer bullets.

The story was not yet over. Federov, the old pioneer and true father of the
intermediate calibre selective-fire rifle concept, now "Doctor of Services,
Professor Lt. General (Technical Engineering Branch) V.G.Federov" and serving as
a senior member of the Technical Council of the NKV, continued to argue for a
smaller-calibre cartridge. As a result, between 1946 and 1948 several different
rounds were made and tested in 6.75mm as well as 7.62mm calibre. Despite this,
the 7.62x39 M1943 cartridge was finally selected in 1948, when the AK-47 was
already undergoing pre-production troop trials. One of the reasons for retaining
the 7.62mm calibre was said to be that the Soviet manufacturing plants did not
at that time have the equipment to mass-produce smaller-calibre ammunition and
gun barrels with the necessary precision.

Some sources claim that the 7.62x39 was no more than a copy of a German Geco
cartridge for the Vollmer M 35 carbine, designed in 1934/35 by the
aforementioned H.G.Winter. However, as we have seen, the cartridges designed for
that gun were quite different, having larger case diameters. The round often
cited as the model for the M1943 is the 7.62x38.5 "Mittelpatrone", but the
diameter of that case is also larger than the M1943's and, according to Dynamit
Nobel (Geco's postwar parent company), it dates from 1960; it appears that it
was in fact inspired by the M1943, not the other way round. There is therefore
no known German cartridge of which the 7.62x39 M1943 could have been a copy. The
authors of a Russian history of the M1943, who had access to Soviet archives,
were unable to find reliable information as to whether the USSR had any previous
knowledge of the development of intermediate rounds in the West.

The next assault rifle to emerge after the StG 44 was the Kalashnikov AK
(above), also chambered for the new M1943 cartridge. There is
still some sensitivity about the connection between the AK and the StG
44, but two things are clear; despite the apparent similarity, the AK
was not a direct copy as it uses a quite different mechanism, but on
the other hand Kalashnikov and his team must have known about the StG
44 (tens of thousands were captured and examples would certainly have
been provided to Soviet small-arms design teams) and it is difficult to
believe that they were not influenced by it, even if only to take it as
a starting point for improvement.

It should perhaps be noted that the term "AK-47" was
applied by the Russians only to the pre-production version of the gun, of which
a few hundred were made for troop trials between 1947 and 1949. Modifications
were then made to the design before it was formally adopted as the AK (Avtomat
Kalashnikova, or automatic [rifle] by Kalashnikov). In 1959 the AK was
replaced in production by the AKM, which was lighter and cheaper due to the
replacement of the machined receiver by one of stamped steel. However, both AK
and AKM have always been popularly if inaccurately known in the West as the
AK-47.

The
AK / AKM and its ammunition (also used in the RPD light MG) so
dominated the assault rifle field until the late 1960s that it is
sometimes difficult to remember that there were other developments, one
of which saw service. This was the Czech vz52 rifle chambered for their
7.62x45 (after earlier experiments with a 7.5x45), a superior cartridge
to the AK's in terms of range, but it was soon replaced by the vz52/57
(chambered for the 7.62x39) in the interests of commonality with the
rest of the Warsaw Pact. The vz52 was only semi-auto, but the Czechs
were working on a selective fire weapon based on the round when the
changeover to the Russian calibre took place; this assault rifle was
the vz58.

Other nations also
experimented with short-case FCAR rounds, particularly the French and the Swiss. Cartridges such as the Swiss 7.62x38, the
French 7.65mm Model 48 (7.92x35 - the French also experimented with calibres up to 9mm)
and the 7.5x43 CRBA of the late 1950s,
plus the Danish 7x36 Madsen or Otterup were all unsuccessful contenders during the 1950s.
Falling loosely into this category were the late-WW2 efforts in Finland, producing such cartridges as the
bottlenecked 9x35 Lahti (in the AL43 - a modified SMG design) and the straight-cased 9x40 Lilja,
but these had light, round-nosed bullets indicating their SMG point of origin.
A 7.62x35 version of the Lahti, with a pointed bullet, was more promising but
still not adopted.

One cartridge worth its own paragraph was the Spanish 7.92x40 CETME
Model 53. The ammunition was designed by Dr Gunther Voss, a German ballistician working for CETME. He wanted to combine a good
long-range performance with light recoil, which he achieved by using a
6.9 g (106.5 grain) bullet made from solid aluminium alloy except for
the copper sleeve around most of its length, which compensated for its
light weight by being highly streamlined. As a result, it achieved a
ballistic performance comparable with the 7.62x51 (MV was 800 m/s from
a carbine-length barrel of 435mm) with a significant reduction in
ammunition weight and an even bigger reduction in recoil.

Another which very nearly saw service was the British EM-2
bullpup rifle, initially chambered for a new .280 cartridge (later with
a slightly modified rim as the .280/30 - both measured 7x43 in metric
terms) which after experiments with 8.4g (130 grain) bullets was
trialled with a 9.0g (140 grain) bullet at 736 m/s (2,415 fps), for a
muzzle energy of 2,440 joules. Unlike the AK, which continued to be
supplemented by the full-power 7.62x54R Nagant cartridge in MGs and
sniper rifles, the EM-2 was a carefully-judged attempt to produce a
weapon which could replace both the 9mm Sten SMG and the full-power
.303 Lee Enfield rifle in one compact package. A GPMG based on the Bren
mechanism but with belt feed, the TADEN, was also developed to use this
round and replace both the Bren and (at least partly) the Vickers MMG.

The EM-2 was
submitted for comparative testing in the competition to select a new standard
NATO rifle/MG cartridge. The result was promising: the 7x43 was regarded by the
US Army's testers at Fort Benning as a better basis for development than the new US .30 cal round
with which it was competing,
and other NATO countries (Canada and Belgium, at least, who both made ammunition) were very interested in the concept.

The British and Belgians made great efforts to
meet the objections of the US Army, who thought it wasn't powerful enough, by
carrying out a lot of work to improve its performance. The first effort was to
step up the velocity to 770 m/s (2,525 fps), followed by seating the bullet less deeply to
make more room for propellant (the 7mm Optimum or 'S'). Longer cases were also
tried: a UK-only High Velocity variant with a 49.5mm case length and a velocity
of about 838 m/s (2,750 fps); then the 7mm Compromise (the new US .30 cal case necked-down,
with a length of 51mm) with a muzzle velocity of about 850 m/s 2,800 fps); then the 7mm
Second Optimum or Medium (the Belgian 7x49 with an MV of 840 m/s (which was the
only one of the series to see service - with Venezuela in the FN FAL
rifle). In all of these, the bullet remained the same weight at 9.0g.

The EM-2 + 7x43 combination appears to have achieved all
that was asked of it, and in 1951, while the above experiments were going on, the cartridge was briefly adopted by the UK as
the '7 mm Mk 1Z' (with the 43mm case length and a 9.0g bullet at 777 m/s - 140
grains at 2,550 fps), at the same time as the EM-2 was adopted as the 'Rifle,
No.9 Mk 1'. However, it faced insurmountable political obstacles. The Americans insisted on NATO
adopting a common round which had to be of .30 calibre and powerful enough to replace the .30-06 in MGs
- which meant by definition that it could not be used in an assault rifle. A
change of government resulted in the British giving way and cancelling the EM-2
and its cartridge in favour of
the FN FAL in 7.62x51 NATO, which apart from being half an inch shorter than the
.30-06 cartridge represented no progress whatsoever over this fifty-year old
design. The EM-2 was reworked to fire the new NATO round, but the heavy recoil
destroyed the balance of the weapon and it went no further.

The
irony was that the stated aim of the US Army was to adopt a lightweight
selective-fire rifle in .30 cal which could replace the M1 Garand
rifle, the M2 .30 Carbine, the .30 cal Browning Automatic Rifle (BAR)
and the .45 Auto M3 SMG. In the event, the 7.62mm M14 rifle could only
replace the Garand; it was too light to replace the BAR and too heavy,
with too much recoil, to replace the Carbine and SMG. Both the 7mm EM-2
and the 7.92mm CETME Model 53 came much closer to meeting the Army's
requirements.

A couple of other peripheral
issues are worth mentioning. An early in-house rival to the .280 was
the .270 (6.8x46) which used a more slender case of similar base
diameter to the .276 Pedersen, the 7.62x39 and the present-day 6.5mm
Grendel and 7x46 UIAC. This was optimised for shorter ranges so fired a
light, 6.48g (100 grain) bullet at 840 m/s (2,750 fps). This was not
good enough at long range, but the cartridge clearly had the potential
to fire a heavier bullet at a still respectable velocity. It would
arguably have made a better basis for a general-purpose round than the
.280, which was biased in favour of very long-range performance to meet
US requirements. It is also worth noting that there is some confusion
over the EM-1, since two different weapons were assigned the same
designation: the first was a full-powered (7.92x57) bullpup gun
by Roman Korsak, a Pole working in England, the second EM-1 was a rival
to the EM-2 in the same 7x43 calibre, which had a similar bullpup
configuration but with a different action and was made from stampings
and pressings rather than machined.

Small-calibre rifle cartridges were in use or under
development for military purposes from very early days. The USN's 6mm Lee of 1895 is probably the
best known, but the curious 5.2mm Mondragon of 1894 was also made (the odd shape
resulting from an internal piston to give the bullet an initial kick up the
barrel) and the 5mm Sturtevant was being developed towards the end of WW1. At
that time the available propellants were not suited to getting the best from
such rounds.

American experiments were made in the 1950s with a
range of smaller calibres, such as the .22 APG (designed for use in a modified
M2 Carbine), .22/30 NATO, the .25/30 NATO (6.35x51) and the .27 NATO (6.85x51), but these led
to nothing.

From left to right: 7.62x51 for scale, 6mm Lee, 5.2mm Mondragon, 5mm Sturtevant

Frustratingly
for the intermediate-calibre supporters, the US Army realised after
initial experience in Vietnam that they had made a mistake and
cancelled further production of the 7.62mm M14 rifle (which had anyway
experienced serious production quality problems). Inspired by
experimental work which showed the efficiency of small-calibre rifles,
they went to the other extreme in adopting the M16 rifle and its tiny
.223 (5.56x45) cartridge (after some competition from the .224
Winchester and two different .25" Winchesters (6.35x48 and 6.35x53).
The 5.56 was developed from Remington commercial hunting rounds which
had been designed for taking small game such as rabbits. This was
actually only intended to be an interim purchase pending the perfecting
of the SPIW flechette rifle (see below) but as this never happened, the
5.56x45 became the US Army's standard rifle cartridge by default. Much
controversy arose about its effectiveness in stopping a determined
enemy, but what was clear was that the long-range performance of the
little bullet (designated M193) was poor. In the next competition for a
new NATO rifle cartridge held in the late 1970s, the 5.56mm was duly
adopted but in the new Belgian SS109 loading (M855 being the US
version), which has a heavier bullet at a lower muzzle velocity and
thereby achieves a better long-range performance and penetration -
although its terminal effectiveness on human targets has been even more
critically questioned. The USA has continued to develop improved 5.56mm
ammunition, recently adopting the lead-free M855A1 Enhanced Performance
Round and (for the USMC) the MK318 Mod 0.

Rather surprisingly, the Russians
were inspired by the 5.56mm to develop a new 5.45x39 7N6 cartridge for their next-generation rifle, the AK74. This is
a bit less powerful than the 5.56 NATO although the bullet does have an exceptionally good
aerodynamic form achieved partly by a hollow tip, giving it a good
performance at long range. There is a small lead
element at the back of the tip which moves forward on impact, causing the bullet
to destabilise quickly. Despite this feature, it is understood that in some quarters the older
7.62mm M1943 round is still preferred.

More recently, the Chinese have
introduced a 5.8x42 calibre for assault rifles and LMGs.
The ballistics seem little different from the 5.56mm,
although it is claimed that it outperforms it, with penetration
superior to the SS109, a flatter trajectory, and a higher retained velocity and
energy downrange. The differences are only marginal, however, as the standard
rifle round is only loaded to 41,500 psi chamber pressure, compared with
55,000-62,000 for the 5.56x45. Furthermore, the emphasis in the bullet design
has been the penetration of body armour; its hardened steel core will punch
through 10mm armour plate at 300m, which is in the same class as steel-cored
5.56mm AP rounds. A heavier loading of the 5.8x42 also exists, for use in the
GMPG and sniper rifles. The most recent development is the introduction of
a new, universal loading of this cartridge (designated DPB-10), intended to replace the earlier
versions. This has a 4.6g bullet at 915 m/s for (71 grains at 3,000 fps).

The SPIW

At one time
great hopes were placed in flechette technology (in principle, a scaled-down APFSDS tank gun round -
APersFSDS?) to achieve an extremely short flight time and flat trajectory
resulting from a muzzle velocity of around 1,200-1,500 m/s. This gives such weapons an
almost ray-gun like performance, with allowances for range, wind-drift and
target movement being hardly needed at normal battle ranges. This was first
seriously proposed in the American Special Purpose Infantry Weapon (SPIW)
project which began in the late 1950s, in which several manufacturers produced weapons using
basically similar ammunition firing a 1.8mm diameter dart with a plastic
"puller" sabot filling the case mouth. The cartridge cases
went through various evolutions (some of them shown here) and AAI's XM645
included primer-actuated unlocking: a
large piston primer was designed to be moved backwards by the chamber pressure
(an
idea previously used in US experiments in the 1930s).

All manner of
rifles from several manufacturers were developed to fire this ammunition,
varying from traditional-looking wood-stocked ones, bullpups, space-age
designs and even multi-barrel guns, some with drum magazines. Accuracy was not as
good as conventional rifles, however, and the cost of the ammunition was very
high. Doubts were also raised about the terminal effectiveness against
unprotected targets (penetration of armour was excellent). Attempting to
achieve everything in one weapon by building in a multi-shot grenade
launcher didn't help. The SPIW project
faded out, eventually closing down in the early 1970s and leaving the "temporary"
5.56x45 with the accidental prize of becoming the USA's, and subsequently NATO's, new
rifle/LMG calibre. There were also several attempts at a multi-flechette weapon;
one example being the .330" Amron Aerojet, another being the 9.53x76R, both of
which contained three flechettes within their
light-alloy cases.

More
Conventional Efforts

Despite the domination of the
5.56mm NATO round (in much of the world) and the Kalashnikov family (in
the rest), experiments with new assault rifle and ammunition concepts
have of course continued, even with the occasional competition being
held. Some of the experiments have been with conventional ammunition,
others have been more exotic. Germany produced an interesting-looking
6.5x43 round in the early 1960s, but only for ballistic testing.

Perhaps the most instructive series of experiments took place in the UK in the late
1960s, when a thorough attempt was made to design an ideal military
small-arms round. This started with calculations of the bullet energy
required to inflict a disabling wound on soldiers with various levels
of protection. The energy varied depending on the calibre, as a larger
calibre required more energy to push it through armour. For example, it
was calculated that while a 7.62mm bullet would need 700 joules to
penetrate modern helmets and heavy body armour, a 7mm would require
650J, a 6.25mm 580J, a 5.5mm 500J and a 4.5mm 320J (this last figure
looks wrong and should probably be 420J). This figures applied at the
target; muzzle energies would clearly have to much higher, depending on
the required range and the ballistic characteristics of the bullet.

A range of
"optimum solutions" for ballistics at different calibres was produced. These
resulted in muzzle energies ranging from 825 joules in 4.5mm to 2,470j in
7mm. More work led to a preferred solution; a 6.25mm calibre with a bullet
of 6.48g at 817 m/s (100 grains at 2,680 fps), for a muzzle energy of 2,160
joules. The old 7mm
EM2 case was necked down to 6.25mm for live firing experiments, although had
the calibre been adopted a longer and slimmer case would have been adopted.
Tests revealed that the 6.25mm cartridge matched the 7.62mm NATO in
penetration out to 600m and remained effective for a considerably longer
distance, while producing recoil closer to the 5.56mm.

As related in The .256 British,
at much the same time, the US Army was looking to develop a new squad
automatic weapon (SAW). The 7.62mm was too powerful, the 5.56mm didn't
have a sufficiently long range, so a 6x45 round was developed which
proved satisfactory but was not adopted because of concerns about
putting a multiplicity of calibres into service. A light-alloy cased
version of this round was also produced, with the length extended to
50mm to make up for loss in capacity caused by the need to line the
inside of the case with fire-resistant material (aluminium alloy having
a tendency to catch fire). The Russians in the 1990s also
unsuccessfully developed various new 6mm cartridges under the "Unified" programme, but these
were considerably larger and more powerful than the 5.45mm, intended to
be used in long-range MGs and sniper rifles. The
Swiss experimented with at least two cartridges in the late 1970s
before adopting the 5.56mm NATO; the 5.6x48 Eiger and 6.45x48 GP 80.
The 5.6mm fired a 3.7g bullet at 1,050 m/s for 2,040J (considerably
more than the 5.56mm NATO) while the 6.45mm managing to propel its 6.3g
bullet at 900 m/s for 2,550J. Both rounds were based on the 12mm-wide
7.62x51 NATO case and were therefore considerably larger than most
other intermediate rounds. With the benefit of hindsight, a heavier
bullet at a more moderate velocity might have provided a better
general-purpose loading for the 6.45mm.

Despite concerns about the stopping power of the 5.56mm, some experimenters have worked with even smaller calibres. The British
proffered a 4.85x49 (actually, 5mm) round for the NATO contest which chose the 5.56mm, the
H&K G11
(described below) used a 4.7mm. Calibres of 4.6, 4.3, 3.5 and 3mm (and
possibly more - or less) have been tried, mainly during the 1960s and
1970s. It is difficult to imagine that such cartridges could do
anything to improve on the 5.56mm's range and stopping power. There is
also the capillary problem with the really small bores; any water which
gets into the barrel will be difficult to dislodge.

A couple of interesting experiments were the 4.6x36 HK for the HK36 rifle (not
to be confused with the current 4.6x30 for the HK MP7, nor with the current HK
G36 5.56mm rifle), which featured a 'spoon tip' to the bullet to encourage
tumbling on impact, and the US 5.56mm FABRL (Frankford Arsenal/Ballistic
Research Laboratories), which combined a light-alloy case with a lightweight
but aerodynamic bullet at high velocity.

The more exotic experiments have proceeded
in different directions, with different aims in mind. Some attempts have been
made to improve the hit probability of conventional 7.62mm cartridges with
multi-ball loadings, using two (duplex) or three (triplex) lightweight bullets
stacked on top of each other. One of these, the US M198 Duplex, was even
accepted for service. A "salvo-squeezebore" (firing several stacked conical
projectiles which were squeezed down to a smaller calibre by a muzzle attachment) was developed for the .50" BMG,
and a version in 7.62x51 NATO was also tested with unsatisfactory results.
7.62mm APDS loadings have also been tried, and one of them has seen service with
the Swedish Army as a sniper round.

Other
experiments have looked at different cartridge types to suit novel gun
designs. Perhaps the most bizarre was the US "folded" ammunition,
stemming from a desire to make the cartridge as short as possible to
speed up the firing cycle. These were made in many calibres, including
5.56mm. Another try was the Hughes Lockless (also made in calibres up
to 30mm) which concealed the bullet within a flat, rectangular plastic
case. This was designed to slot sideways into a simple gun action.
Other oddities were the Belgian Schirnecker rounds of various sizes
which fired saboted bullets from straight steel cases, and the 9/4mm
Kaltmann in which the plastic cartridge case was expected to follow the
bullet down the barrel.

The closest to adoption of all of the exotics was the caseless
cartridge, in the form of the Heckler & Koch G11 rifle. It
was actually about to be adopted by the German Army to replace the 7.62mm G3
(Germany never having adopted the 5.56mm NATO) when the Cold War ended and the
Berlin Wall came down. Military re-equipment spending promptly halted. H&K were financially ruined by
the cancellation of the G11 and temporarily fell into the hands of Royal Ordnance, where
they earned their keep by sorting out the long-running problems of the
British Army's SA-80 rifle, but that's another story. In 2002, HK were taken
back into German ownership. Caseless 5.56mm rounds had also been experimentally
developed around 1970 in the USA, and the Austrian firm of Voere even managed to
sell some commercial caseless rifles in various calibres but these are no longer offered.

Caseless ammunition has obvious
benefits. It is much lighter and more compact (no metal case plus
compressed propellant), and it is unnecessary to arrange for the
extraction and ejection of the fired case (perhaps the principal source
of weapon jams). The disadvantages are that it is much more vulnerable
to damage (which H&K got around by supplying the ammunition in
sealed plastic see-through packs which clipped directly to the gun),
sealing the breech against gas escape is more difficult, and the
propellant is more likely to "cook-off" in a hot chamber; a problem
exacerbated by the fact that a brass cartridge case transports some
heat from the gun. Despite this, H&K (or rather Dynamit Nobel)
developed a new heat-resistant kind of propellant, although at great
cost. The current effort to use exotic technologies, the US Army's LSAT
programme (described below), has explored caseless ammunition based on
Dynamit Nobel's work, but is finding plastic-cased ammunition easier to
work with.

The ACR programme

Flechette
weapons were revived by two of the competitors in the Advanced Combat
Rifle (ACR) contest of the late 1980s. This contest was intended to
improve the poor hit probability achieved by average soldiers in the
stress of battle, which using the M16 was only guaranteed (pH = 1.0) at
up to 45m, and dropped to a pH of 0.1 (one shot in ten) by 220m. The
theory was that firing three slightly dispersed shots in quick
succession should enable the pH to be doubled, and several different
weapon concepts were prepared.

The Colt ACR contender was simply an improved M16A2 firing a duplex cartridge,
and H&K submitted the caseless G11 described above, while AAI and Steyr
offered weapons firing flechette rounds, the Steyr ammunition being
plastic-cased.

Although all of the weapons apparently performed well and
did increase the hit probability, none of them managed to double it, so this
once again proved a dead end.

Despite all of these experiments,
small arms currently in service are relatively conventional, at least as far as the assault rifle
element is concerned. With the break-up of the Warsaw Pact, several East
European nations have switched to 5.56mm NATO weapons, either bought-in or
of their own design. Even Russia is now offering Kalashnikovs for export
sale in 5.56x45 as well as its domestic calibres.

The US Army has switched to the M4,
a carbine version of the M16 with a shorter barrel. In 2012 US
planned two parallel programmes: a product-improved M4 in competition
with a separate contest for a new Individual Carbine. The contest was
cancelled in 2013, leaving the improved M4A1 (with a heavier barrel and
a full-auto rather than burst-fire switch) as the Army rifle for the
foreseeable future.

The US Special
Operations Command (SOCOM)
selected the FN SCAR rifle/carbine in Light (MK16 in 5.56x45) and Heavy
(MK17 in 7.62x51) versions, although they are currently focusing just on the
MK17. Heckler & Koch has achieved sales success with the G36 and now also offers paired 5.56mm and 7.62mm
weapons, the HK416(adopted by the USMC as the M27 Infantry Automatic Rifle) and HK417 respectively, as does Colt with
its CM901
which can be converted from one calibre to the other. Several other
countries have also been developing new 5.56mm rifles, notably Beretta
in Italy with the ARX-160, plus Poland with the modular MSBS (interestingly, planned to be available in traditional and bullpup forms) and the Czech
Republic with the CZ-805 Bren (reviving a famous name), plus others in Asia and the Americas.

All these weapons
(except the MSBS) use a traditional instead of bullpup layout, in contrast to the
Chinese QBZ-95, the Israeli Tavor,
the SAR-21 from Singapore the FN2000 and the first 5.56mm bullpup to enter service, the Steyr AUG,
which is still offered in updated form. All of these weapons except
for the 5.8mm QBZ-95 are chambered for the usual 5.56x45 NATO.

The
traditional layout is preferred by many as it is easier to switch sides and
use left-handed, but it carries the penalty of a much shorter barrel for the
same overall length. The problem
with short barrels in this calibre is that they reduce the muzzle velocity,
and the 5.56mm bullets rely on a high impact velocity to yaw on impact and fragment
(something which is not guaranteed with the SS109/M855 ammunition, even from
rifle barrels). At lower velocities the bullets are even less likely to
fragment and much of the wounding potential is lost. The US Army's current
preference for the short-barrelled M4 has restarted this argument,
with the terminal effectiveness of the 5.56x45 becoming controversial once
again. The pros and cons of the bullpup vs traditional layout are explored
HERE.

The photo below shows the HK416 at the top, the HK417at the bottom and the experimental HK416/6.8mm in the middle.

The Lessons

What conclusions can we draw from all this?

One conclusion as a result of recent combat experience is that the
5.56mm weapons are most effective in short-range combat. That was satisfactory
in Iraq which mainly saw urban fighting, but was revealed as a major deficiency
in the much longer ranges common in Afghanistan. The British and US Armies both
found that the 300-400m maximum effective range of 5.56mm weapons was inadequate
when foot patrols were engaged by small
groups of Taleban, using 7.62x54R SVD rifles and PKM LMGs at ranges of up to 900m. As a
result, 7.62mm rifles and MGs have made a comeback at section level in the foot
patrols.

In addition, performance of the small-calibre, high-velocity rounds (especially the 5.56mm
NATO) is erratic; sometimes they work well, sometimes they don't, depending on
their impact velocity, the precise manufacturing details and the angle at which
they strike the target. There is more on the subject of small-arms terminal
effectiveness HERE. The 7.62mm weapons are
more reliably effective but are much heavier (both guns and ammunition),
and the recoil of the rifles is also heavy, making automatic fire uncontrollable.

A larger-calibre, more powerful
cartridge than the 5.56mm, but still significantly lighter than 7.62mm
and generating light enough recoil to permit controllable automatic
rifle fire when required, might also deliver another substantial
benefit: its performance could be close enough to that of the 7.62mm
NATO to permit the new cartridge to replace both existing 5.56mm and
7.62mm rounds, providing considerable benefits in reducing the weight
of MG ammunition plus the costs of small-arms acquisition, training and
support. The August 2011 report by the US Army's PEO Soldier report
titled Soldier
Battlefield Effectiveness includes a number of points in favour of
general-purpose weapons and ammunition, summarised concisely in this:

"Ultimately, Army
service rifles must be general purpose in nature and embody a series of
tradeoffs that balance optimum performance for a wide range of possible missions
in a range of operating environments. With global missions taking Soldiers from
islands to mountains and jungles to deserts, the Army can’t buy 1.1 million new
service rifles every time it’s called upon to operate in a different
environment."

Is it possible to achieve a suitable
general-purpose
cartridge? The evidence suggests strongly that it is. A 2010
investigation into rifle calibres by the US Army's ARDEC compared cartridges in
5.56mm, 6mm, 6.35mm, 6.8mm and 7.62mm calibres and determined that, when
considered across a range of criteria, the 6.8mm offered the best compromise
with the 6.35mm following closely behind, both of these being clearly ahead of
the others. In 2012 the US Army's Marksmanship unit (AMU) carried out its own
investigations into the optimum cartridge for future military rifles and
concluded in favour of 6.5mm.

The British aimed for this with
the 7x43 cartridge half a century ago, and by all accounts succeeded
admirably. This gives us an upper calibre limit. It seems unlikely that
a cartridge with the long-range performance and hitting power to
replace the 7.62mm can
be achieved with anything smaller than 6.5mm calibre, which gives us
the lower limit. We need to specify a bullet with a ballistic
coefficient significantly better than the 7.62mm's M80 bullet to
deliver the long-range performance we want. We also need a
muzzle energy of about 2,500 joules to provide the right balance
of power and recoil. These issues are explored in more detail HERE.

Long after writing this section, I discovered an old scrap
of paper on which I had jotted down a proposed "General Purpose Cartridge" in
1971. At that time I was a youngster who knew nothing of the 6mm SAW or 6.25mm
British experiments which were then underway, but my proposal was remarkably
similar to the conclusions I reached in writing this article: a 6.5x45 GPC with
a body diameter of about 10.5mm and an overall length of 65mm, firing a 120
grain bullet at 2,600 fps. I quote this not in order to demonstrate my
precocious prescience, but to illustrate that the characteristics of the optimum
compromise cartridge are quite obvious to anyone who takes a passing interest in
the subject. For anyone interested, the paper is HERE.

One important point which needs to borne in mind, however, is the current trend
towards using lead-free ammunition. Bullets with cores of copper or steel need
to be longer than lead-cored bullets of the same weight, and since low-drag
6.5mm bullets are rather long anyway, making them lead-free could cause
technical problems - especially given the need for even longer tracer bullets.
This suggests a larger calibre might be preferable, possibly 6.86mm.

The current
contenders

So, we have identified the basic parameters of an
ideal military general-purpose assault rifle and LMG cartridge - and we could
have had it many decades ago. What are the chances of such a cartridge being
adopted now? Some hopes were raised recently by the introduction of a couple of
new rounds which (more or less) fit the above criteria. One is the 6.8x43
Remington SPC (Special Purpose Cartridge) which fires a 115 grain bullet at
2,650 fps from a 16.5 inch barrel (7.45g at 808 m/s = 2,430J). The cartridge case is based on the old .30
Remington commercial round, with a diameter of 10.6mm, intermediate between the
5.56x45 (9.5mm) and the 7.62x51 (11.9mm). Overall length is kept within the 57mm
limit to fit in the M16 action, which limits the length of the bullets which can
be loaded, blunting their long-range performance. Even so, this round develops
55% more muzzle energy than the 62 grain SS109/M855 loading at the muzzle,
rising to 84% better at 550m due to its superior ballistic coefficient. The trajectory matches that of the 7.62x51
M80 ball out to 500m, and is only 10cm low at 600m. The development of this
round was sponsored from within the US SOCOM (Special Operations Command)
who were looking for a more powerful cartridge than the 5.56mm, and it has
reportedly been successfully tested in action, although not adopted for logistic
and financial reasons. SOCOM, and now the USMC, has instead adopted the 5.56mm
MK318 Mod 0 SOST ammunition, which is reportedly much more effective but uses an
open-point bullet unacceptable to UK and probably other European countries. In
any case, while the 6.8mm Remington would be a significant improvement over the
5.56mm, it does not have the range to replace 7.62mm and thus could not be a
general-purpose cartridge.

More
recently, another challenger emerged in the form of the 6.5mm Grendel
(6.5x38).This uses a slightly fatter case (the same 11.3mm diameter as
the 7.62x39 Russian) which enables it to be shorter, thereby leaving
space for longer and more aerodynamic bullets. This enables it to fire
a 123 grain Lapua Scenar bullet at 2,530 fps (8.0g at 770 m/s: 2,370J)
from a 16 inch barrel, with a far superior ballistic coefficient to the
5.56mm Mk 262 or 6.8mm bullets (SD 0.252). In a longer rifle or MG
barrel this provides trajectory and velocity loss figures to match or
better those of the 7.62x51 M80 ball round. This clearly has potential
for a general-purpose cartridge, but there are some reservations. The
performance shown below is achieved with a high-quality target bullet;
a military ball round with a crimping cannelure would not have such a
good ballistic coefficient. Also, adopting a lead-free design would
significantly lengthen the bullet (and a tracer even more so) so it
would have to protrude more deeply into the case, reducing the
propellant capacity. And the shape of the case may be rather stubby to
be ideal in a belt-fed MG. It is however, the closest to a
general-purpose rifle/LMG cartridge commercially available.

The photo
shows the 5.56x45 M855A1, 6.5x38 Grendel, 6.8x43 Remington SPC and 7.62x51
M80, with their bullets. Note the bullets beside the 5.56mm: the new M855A1
(with an exposed steel tip) has the lead core element replaced by copper,
resulting in a significant increase in length to achieve the same weight as
the SS109 next to it. The other bullets are all lead-cored; note the much
more aerodynamic proportions of the 6.5mm compared with the others
(especially the rather stubby 6.8mm)

The designs of both the 6.8mm Remington and the 6.5mm Grendel
have been compromised by the need to keep within the 57mm overall length of the
5.56x45, so that existing 5.56mm weapons can be rebarrelled to chamber them. A
clean-sheet design would probably result in an overall length of around
65mm.

Another new round
currently being developed by Cris Murray, who was involved in the 6.8mm
Remington development, is the 7x46 UIAC (Universal Intermediate Assault
Cartridge). This is based on the same 11.3mm case diameter as the 6.5mm
Grendel. In its proposed standard loading it fires a 130 grain bullet at
2,650 fps (8.4g at 810 m/s). This develops 2,750 J, so it is very much at
the top end of the size, calibre and power range. The extra case width over
the 6.8mm Rem's 10.6mm might however prove useful in accommodating long,
lead-free bullets and possibly thicker cases made from polymer, should these
succeed in meeting military requirements. Interestingly, the basic case
dimensions of the UIAC are very similar to those of the .270 British from
the late 1940s, and the performance is very similar to that of the .276
Pedersen of the late 1920s.

Of the current rounds, the 7mm UIAC
and the 6.5mm Grendel represent the top and bottom of the range for a
general-purpose rifle/MG round in terms of their performance, recoil,
calibre, size and weight. Perhaps the ideal lies somewhere in between?

The US Army has for several years been funding the Lightweight Small Arms
Technologies (LSAT
) development programme, with the aim of halving the weight of
the current 5.56 mm M249 (FN Minimi) LMG and its ammunition. The AAI Corporation
(now Textron) is the lead contractor for the project and is responsible for the gun design. Two different
cartridge designs have been tested, shown below in comparison with existing
rounds. One is a polymer-cased telescoped round (by ARES) now in "Spiral 3"
- the third generation,
the other a caseless round (by ATK) based on HK G11 technology. The caseless
rounds save 38% in volume, and weigh 6.3g each compared with c.12.2g for the
M855 to give overall weight savings of 51% (due to the lighter plastic belt
links). The plastic-cased Spiral 3 rounds are 40mm long by 11.4mm in diameter
and save just 13% in volume, and weigh 8.3g. They save 41% in weight in MG belts
compared with M855 belts, due to the plastic links which weigh 0.5g compared
with 2.0g for the steel links. Total weight of a 200-round belt of Spiral 3
ammunition is 1.76kg compared with 2.84kg for M855.

A belt of 5.56x45 is shown next to LSAT belts:
caseless (centre) and plastic-cased Spiral 3. Plastic belt links help to
save weight.

Above: the LSAT LMG

The emphasis has been on
developing LMGs, but there was a programme to develop a carbine to
use the same ammunition. The first SN1 model (a mock-up of which is shown below)
was test-fired in May 2010 and has been tested at TRL 5. This used an
interesting mechanism which withdraws the rounds backwards from the magazine,
resulting in a longer barrel length for a given overall length: the saving in
length is about 100mm compared with 200mm achieved by a bullpup layout. A second
model of carbine (SN2) was being prepared for firing tests in mid-2011, with the
aim of offering M16 performance at M4 weight and length. However, the carbine project has been suspended.

Above: a dummy of the first LSAT carbine

While the caseless ammunition is both lighter and more compact than the plastic-cased, the
usual technical problems experienced with such ammunition has led to the
emphasis being placed on the latter. By mid-2011 some 400 caseless rounds had
been fired with a TRL 5 demonstration planned for the autumn. In contrast, some
14,000 plastic-cased rounds had been fired through four LMGs, and eight LMGs
plus 100,000 rounds of plastic-cased ammunition (loaded with M855A1 bullets) were supplied to the US Army for
initial testing in autumn 2011. Initial informal reports indicate that this seems to have gone well, but the cost of
establishing new production facilities for both guns and ammunition will clearly
be a major obstacle to adoption.

LSAT 5.56mm and 7.62mm, next to the 5.56x45 and 7.62x51 (image courtesy of Textron)

The
initial
calibre and ballistics of LSAT were chosen to match the 5.56x45
SS109/M855 for comparison purposes but, more recently, a 7.62mm LSAT
has been demonstrated whch matches the performance of the 7.62x51 while
reducing the weight by 33% (39% in MG belts because of the plastic
links used). However, it appears that
consideration is being given to developing an
intermediate calibre cartridge which might replace both the 5.56mm and
the 7.62mm, with funding continuing at a low level to pursue this. And the
initially suggested characteristics of
this new cartridge? 6.5mm calibre, firing a 120 grain bullet which matches the
effectiveness of the 7.62x51 at 1,000m. This is beginning to sound familiar...

Future Options

In the near
term, attention is now focusing on the next generation of infantry
small arms, for 2025 and beyond. This is the date currently envisaged
by both the US and British Armies for the replacement of their families
of 5.56mm weapons. What is the chance of the new weapons being in a new
calibre?

The key to this is of
course the USA, since it is unlikely that any NATO nation will adopt a
new rifle/MG cartridge unless the US Army does so first. At the moment, the
only new cartridge on the horizon is the LSAT. If this fails to be adopted, any new
conventional cartridge would have a harder battle to achieve
acceptance since the argument will always be that any benefits from a
new round will be reduced by disadvantages (e.g. greater bulk, weight
and recoil than the 5.56mm), so the changeover would not be worth the
huge cost. A counter-argument to this lies not just with the weight
savings over the 7.62mm, but also the development of computerised rifle
sights such as the US DInGO which will enable ordinary riflemen to
accurately engage targets out to the sort of ranges currently reserved
for snipers - provided the gun and ammunition are capable of such
ranges.

Any
conventional cartridge - new or existing - would by then almost
certainly use some form of lightweight case to bring down the
ammunition weight. The current front-runner is a polymer case body with
a metal reinforcement at the base to take the stress of extraction.
These have been tried before and failed, but the US firms PCP and MAC
LLC are using new technology which they claim will meet military
requirements for heavy use in MGs. Weight savings won't be quite as
spectacular as with LSAT, but they will still be well worth having.

Within the foreseeable future the current
metal-cased ammunition may therefore be replaced by something a lot lighter and
possibly more compact. If that happens, let's hope that the military takes the
opportunity to adopt something like the "optimum compromise" discussed above. The
work done in the USA by ARDEC and AMU has gone a long way to
identifying the optimum calibre and other ballistic characteristics of
any new rifle/MG round.It would be a tragically wasted
opportunity if their work is ignored and the next generation of NATO small-arms is designed around the
5.56mm and 7.62mm, just because that's what we have, when we know that we could
do much better.

A more detailed examination of the
case for a new intermediate rifle/MG round is
HERE

A follow-up article looking at the
characteristics of the next generation of military small arms is
HERE

Readers wishing to learn more about
this subject will be interested in 'Assault
Rifle: the Development of the Modern Military Rifle and its Ammunition'
by Maxim Popenker and Anthony G Williams. Details are
HERE

Sources:

Hogg, I and Weeks, J. Military Small Arms of the 20th century

Dugelby, T.B. Modern Military Bullpup Rifles

Long, D. Combat Rifles of the 21st Century

Stevens r. and Ezell, E. The SPIW: The Deadliest Weapon That Never Was